Two important viruses, human lymphotropic leukemia virus III ((HTLV-III) which causes the acquired immune deficiency syndrome and cytomegalovirus (CMV) which is responsible for cmv disease which is responsible for CMV disease induce immunosuppression in vitro and in vivo. However, which causes the acquired immune deficiency syndrome the role of monocytes/macrophages in this immunosuppression is unknown. Therefore, the goal of this project has been to determine whether these viruses can infect human monocytes and whether infected monocytes exhibit impaired effector cell function and/or antigen-presentation. The results obtained thus far indicate that both HTLV-III and CMV can infect human monocytes. Furthermore, viral-infected monocytes appear to have impaired cell functions including cytotoxicity, chemotaxis, inflammatory mediator (interleukin-1, prostaglandin E2) production and antigen-presentation. This information indicates that the monocyte/macrophage likely contributes to the in vivo immunosuppression caused by HTLV-III and CMV.